Bio balls are used instead of heavy lava rocks as a filter material in a pond biological waterfall filter. Bio Balls have 44 square feet of surface area compared to lava rocks that only have 16 square feet of surface area for beneficial bacteria to grow on. The biological filter is a very important piece of your pond fitration system. Replacing the lava rock in your Biofalls filter with Bio balls will increase the biological filters capacity, improving your filter system! You should also notice an increase in water flow from your Biofalls filter because the bioballs have less resistance than lava rocks. One cubic foot of bio balls only weighs 5 pounds, lava rock on the other hand can weigh over 40 pounds per cubic foot! Because bioballs are so light, lifting them up to gain access to the filter pads below them is very easy. Bio Balls never need to be rinsed off! lava rocks do need to be rinsed off because they will clog with dirt and debris reducing the active surface area for good bacteria to grow on. Bio Balls sink, are black in color, and fit perfectly inside black mesh bags for easy lifting. These are a must have for your Aquascape Designs Biofalls Filter! How many Bioballs do I need? 1 cubic foot for the micro biofalls filter. One mesh bag is needed for this amount. 1.5 cubic feet of Bio Balls for the Aquascaepe mini Biofalls filter. One mesh bag is needed for this amount 3 cubic feet of bio balls for the Aquascape standard Biofalls filter. Two mesh bags are needed for this amount. 5 cubic feet of bio balls for the Aquaacape Grande Biofalls filter. Four mesh bags are needed for this amount. 1 Cubic foot for the new Aquascape Signature Series Biofalls filter 2500. One mesh bag is needed for this amount. 2.5 Cubic Feet for the new Aquascape Designs Signature Series Biofalls filter 6000. Two mesh bags are needed for this amount. Aprox. 400 Bioballs per cubic foot. These bioballs can only be found at PondDepot.com Bio Balls Per Cubic Foot Bio Balls 1.5 cubic Feet Black Mesh Bag ponddepot@msn.com Copyright - All World Rights Reserved Pond bacteria, Pond Kits and Pondless Waterfall kits, Filter Pads, Underwater Pond Lights. pump replacements and pond algae control. Pond Depot provides excellent technical assistance and fast shipping for all orders. The staff at Pond Depot are highly trained and experienced in installing and maintaining ponds. We will gladly answer any questions that you have. Pond Depot your online pond superstore!